Machining process for a gauging or measuring head

ABSTRACT

Gauging head and apparatus for linear dimension checking of mechanical pieces comprising an integral element that defines an arm carrying a feeler, a reference portion, and a fulcrum that enables rotations of the arm with respect to the reference portion, and a differential transformer position transducer with a cylindrical shaped casing, carrying windings, fixed to the reference portion, and a ferromagnetic core movable together with the arm. The integral element is locked in an adjustable way to a support by means of the cylindrical casing. The integral fulcrum is achieved by work hardening the material and subsequently grinding it.

TECHNICAL FIELD

[0001] The present invention relates to a gauging head suitable forcoupling to a support for the linear dimension checking of a mechanicalpiece, comprising a shaped element defining a first reference portion, asecond portion, or arm, movable with respect to the first, and anintermediate portion, or fulcrum, between the first and the secondportion, that defines a geometric axis of reciprocal rotation betweensaid first and second portion, a feeler fixed to said arm for contactingthe piece to be checked, and a transducer device for providing signalsresponsive to the position of the feeler with respect to the referenceportion, including two reciprocally movable parts, a first part thereofbeing stationary with respect to said first portion of the shapedelement, and a second part being movable, together with said arm, withrespect to the first portion.

[0002] The invention also relates to a checking apparatus for the lineardimension checking of a mechanical piece, comprising a support, agauging head with a shaped element defining a first reference portion,stationary with respect to the support, a second portion, or arm,movable with respect to the first, and an intermediate portion, orfulcrum, between the first and the second portion, that defines an axisof reciprocal rotation between said first and second portion, a feelerfixed to said arm for contacting the piece to be checked, and atransducer device for providing signals responsive to the position ofthe feeler with respect to the reference portion, including tworeciprocally movable parts, a first part thereof being stationary withrespect to the first portion of the shaped element, and a second partbeing movable, together with said arm, with respect to the firstportion, and a processing unit, electrically connected to the transducerdevice.

[0003] Furthermore, the invention relates to a process for machining thearmset of a gauging, or measuring, head including an integral elementthat defines two reciprocally movable portions and a fulcrum betweensaid portions.

BACKGROUND ART

[0004] There are known gauging heads for the geometric inspection ofmechanical pieces that comprise a measuring arm with a feeler forcontacting a piece to be checked, an element for supporting the arm, afulcrum for allowing displacements of the arm with respect to thesupport element and a transducer for providing a signal responsive tothe position of the arm with respect to the support element, in whichthe measuring arm, the support element and the fulcrum are formed from asingle piece.

[0005] An example is provided in U.S. Pat. No. U.S. Pat. No. 4,409,737,that discloses gauging heads in which the support element comprises awing, that extends in a direction perpendicular to the arm and enablesthe coupling—by means of screws—of the head to an external support. Thistype of coupling is quite lacking in versatility, in that, as thenominal dimensions of the piece to be checked vary, generally there isthe need to replace the feeler and/or couple—by means of screws—the headin another area of the support or to another external support. In orderto guarantee the correct operation of the head, the coupling existingbetween the wing and the external support must be extremely accurate.This involves precision mechanical machinings of the surfaces intendedto be arranged into mutual contact for defining the position of thehead, and particular care in coupling the head to the external support.

[0006] Moreover, in the measuring heads disclosed in the US patent, thearrangement of the fulcrum, feeler and transducer is such that thefeeler displacements occurring further to contact with the surface ofthe piece to be checked and the displacements among the reciprocallymovable parts of the transducer substantially occur along two parallelstraight lines, but at a certain distance from each other. Consequently,the entity of the displacement of the elements of the transducer differsfrom that of the corresponding displacement of the feeler and, in orderto process the correct detecting, it is necessary to keep into accountthe so-called “arms-ratio”, i.e. the ratio existing between the distanceseparating the transducer and the feeler from the axis of rotationdefined by the fulcrum. It is understood how undesired displacements inthe position of the axis of rotation of the arm (due to a not entirelyaccurate implementing of the integral fulcrum) and/or flexions of thearm may negatively affect the operation of the head, modify the ratiobetween the feeler and the transducer displacements with respect to thetheoretical condition that considers an “arm ratio” evaluated on thebasis of the head geometry.

[0007] The type of material utilized in the heads with armsets andso-called “integral” fulcra normally undergoes a hardening process forthe purpose of increasing its ultimate tensile stress and thus itsresilient range. This process, apart from being expensive, is subject toother drawbacks. In fact, when the material is ground for thinning it atthe point where it is desired to achieve the fulcrum, especially if itis desired to attain a very thin fulcrum, there is the risk that thematerial may considerably heat up at the thinned point, and thus loosethe effects that the hardening process had provided. The materialsutilized for hardening must contain carbon and, owing to the fact thatthey are consequently oxidable, need a final treatment, like, forexample, zinc plating.

[0008] It is absolutely necessary to employ particularly yielding, andthus very thin, fulcra when it is required to check pieces havinglimited stiffness that could deflect under a high measuring force, orpieces made of a soft material, that could get scratched.

[0009] Because of the need to accomplish precision mechanicalmachinings, hardening, grinding and subsequent antioxidant treatment, itis evident that these gauges are expensive and it is often difficult toattain particularly thin and yielding fulcra.

DISCLOSURE OF THE INVENTION

[0010] An object of the present invention is to provide an extremelyaccurate, versatile, simple to manufacture and inexpensive gauging headthat overcomes the limitations of the known gauging heads.

[0011] It is another object of the invention to provide a gauging headthat has a measuring force low enough to permit its use even forchecking resilient pieces.

[0012] These and other objects are achieved by a gauging head accordingto claim 1.

[0013] Yet another object of the present invention is to provide achecking apparatus for checking the linear dimensions of mechanicalpieces that, apart from guaranteeing considerable accuracy, is extremelysimple and can rapidly and easily be adapted for checking pieces thathave different nominal dimensions.

[0014] This and other objects are achieved by an apparatus according toclaim 15.

[0015] A considerable advantage that a gauging head and a checkingapparatus according to the invention provide is the utmost flexibility,that enables to employ as transducer devices, both known gauges ofvarious types (axial-sliding or “cartridge” heads, dial typecomparators, or others), and plain transducers (for example, LinearVariable Displacement Transducers, i.e. “LVDT” transducers) withwindings and a ferromagnetic core coupled to the reciprocally movableparts of the armset, respectively. In this second case, an additionaladvantage that the heads according to the invention (and the apparatusesutilizing these heads) provide, is the friction free operation of thevarious moving, component parts.

[0016] An additional object that the invention provides is the attainingof an armset employed in gauging (or measuring) heads, that is extremelysimple from a structural point of view, and can be manufactured byequally simple, rapid and economically convenient machinings.

[0017] This and other objects and advantages are achieved by a processaccording to claim 19.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The invention is now described in more detail with reference tothe enclosed sheets of drawings, given by way of non limiting example,wherein:

[0019]FIG. 1 is a partly cut-away longitudinal cross-sectional view of achecking apparatus comprising a gauging head according to the inventionwith some details shown in front view,

[0020]FIG. 2 is an enlarged scale sectional view of a detail of the headshown in FIG. 1, viewed along line II-II with some parts omitted for thesake of simplicity, and

[0021]FIG. 3 is a partly cut-away longitudinal cross-sectional view,with some details shown in front view, of a gauging head according toanother embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0022] The checking apparatus shown in FIGS. 1 and 2 comprises a gauginghead with an armset basically consisting of an integral, substantiallyU-shaped, element 1, formed, for example, from a single bar of stainlesssheet-steel. The element 1 includes a first reference portion 3 that hasa substantially rectangular cross-section and a second portion, or armS, also with a rectangular cross-section. The arm 5 and the referenceportion 3 are formed by bending the stainless sheet-steel bar.

[0023] An intermediate portion 13, located between the arm 5 and thereference portion 3, has a round-shaped recess 9 and a squared groove11, formed at two opposite sides of the sheet, at a same area, bycompressing or drawing (for example, on a press) and grinding,respectively. In this way, the intermediate portion 13 has a transversalthickness that is reduced with respect to that of the other portions ofelement 1 and forms a fulcrum, in other terms it defines a geometricaxis of rotation for the displacements of arm 5 with respect to thereference portion 3. Portion 13 also has a through hole 14 forincreasing the compliance of the fulcrum.

[0024] The upper end of arm 5 has a bent portion 15.

[0025] The upper end of the reference portion 3 has a part 17 bent andwithdrawn into itself.

[0026] On the bent portion 15 of arm 5 there are two threaded holes 21and 23, aligned with respect to each other. A tang 24 of a feeler 25 forcontacting a mechanical piece 26 to be checked is screwed in hole 21.

[0027] A transducer device comprises a linear variable displacementtransducer 27 with a core 32 made of ferromagnetic material and windings34 that house the core. In hole 23 there is screwed a pin 28 to whichthere is glued a stem 30 that carries the core 32 of the transducer 27.

[0028] On part 17 of reference portion 3 there is a threaded hole 33 andtwo through holes 29 and 31 aligned with respect to each other and thethreaded holes 21 and 23.

[0029] The transducer 27 comprises a casing 35 with an elongate shape,for example a cylindrical shape, that houses the windings 34, and ishoused in the opening defined by the two holes 29 and 31. Lockingelements including a screw 36, that is screwed into the threaded hole33, enable the casing 35 to be locked to the reference portion 3 in anadjustable way along a transversal geometric axis of adjustment definedby the casing 35 itself.

[0030] The windings 34 of the transducer 27 are electrically connected,by means of a cable 37, to a power supply, processing and displaydevice, schematically shown and identified by reference number 38 in thefigures.

[0031] A tubular sealing gasket 39, made of rubber, has an end coupledto arm 5 at the bent portion 15 and the other end coupled to the casing35, so as to protect the transducer 27 from potential damage caused byforeign matter.

[0032] Arm 5 has a cylindrical seat 41 aligned with a threaded hole 43located in reference portion 3.

[0033] Thrust devices between the arm 5 and the reference portion 3 ofthe shaped element 1 comprise a compression spring 45 with an end housedin the cylindrical seat 41 and the other end coupled to a bushing 47,internally threaded. A dowel 49 has an end screwed into the threadedhole 43 and the other end screwed into the interior of bushing 47. A nut50 abuts against the surface of arm 5 for axially clamping dowel 49.

[0034] By operating bushing 47, it is possible to set the thrust ofspring 45 between arm 5 and the reference portion 3.

[0035] The rotations of arm 5 with respect to the reference portion 3are limited, in a clockwise and counterclockwise direction (withreference to FIG. 1), by a mechanical limiting device comprising a screw51 with a threaded stem that traverses a through hole 53 in arm 5 with asuitable amount of radial clearance and is screwed into a threaded hole55 of the reference portion 3. On the stem of screw 51 there are screwedthree nuts 57, 59 and 61. Nut 57 is urged against the reference portion3 for preventing the accidental unscrewing of screw 51. Nut 59 has abase that defines an abutting surface for abutting against an internalsurface of arm 5 for limiting the range of the rotational displacementsof arm 5 in a clockwise direction (with reference to FIG. 1) and nut 61is urged against nut 59 for axially locking nut 59 to the stem of screw51. The rotational displacements of arm 5 in a clockwise direction (withreference to FIG. 1) are limited by contact occurring between theabutting surfaces of the head of screw 51 and the arm 5 itself.

[0036] Moreover, the checking apparatus shown in FIG. 1 includes asupport 67 locked, by means of screws 71, to a base, schematically shownand identified by reference number 72. As shown in FIG. 2, in the upperpart of the aforementioned support 67 there is an opening 73 for accessto a substantially cylindrical hole 75 and two holes 77 and 79, one ofthe two—77—being threaded, aligned along a direction perpendicular tothe axis of hole 75. The gauging head, more specifically the shapedelement 1, is locked to support 67 by first inserting cable 37 throughopening 73, by inserting the casing 35 in hole 75 and then locking thecasing 35 in the required position, by narrowing opening 73. This isdone by inserting a screw 80 into hole 79 and screwing it into threadedhole 77. The holes 75, 77 and 79 and screw 80 taken together form alocking/unlocking device that operates on a coupling surface 40, definedby the cylindric casing 35, for locking, in an adjustable way along thetransversal geometric axis of adjustment, the position of the gauginghead with respect to support 67.

[0037] The checking apparatus, for checking the diametral dimensions ofa shaft 26, for example, operates in the following way.

[0038] Under rest conditions, the reciprocal position between arm 5 andreference portion 3 is defined by the arrangement of screw 51, and, morespecifically, the contact—under the thrust of spring 45—between externalsurfaces of arm 5 and the reference surface of the head of the formerlymentioned screw 51.

[0039] By slackening nut 57 and operating screw 51, it is possible toset the formerly mentioned reciprocal position between arm 5 andreference portion 3, whereas by slackening nut 61 and operating nut 59,it is possible to vary the maximum amplitude of rotation of arm 5commencing from the rest condition.

[0040] In a first zero-setting phase of the gauging head, the pre-strokeis defined, i.e. the distance that the feeler must travel, commencingfrom the rest condition, before it reaches zero position. In order to dothis, the reciprocal position, under rest conditions, between core 32and windings 34 of the transducer 27 is defined by operating the lockingelements, more particularly by slackening screw 36 and adjusting theaxial position of casing 35 until the display unit 38, that receives andprocesses the associated signals issued by transducer 27, indicates therequired pre-stroke value, for example 300 μm. At this point, screw 36is clamped onto the coupling surface 40 of casing 35 for setting theposition of the latter on the integral element 1. The head is thencoupled to support 67, by inserting the casing 35 in hole 75. A masterpiece, with a diameter size equal to the nominal one of the shafts to bechecked, is positioned between reference supports, not shown in thefigures, for example, Vee-shaped supports, stationary with respect tothe base 72, in such a way that feeler 25 contacts the surface of themaster piece in a diametral direction. Then, casing 35 is axially slidinto hole 75 until, further to contact occuring between feeler 25 andthe surface of the master piece and the feeler subsequently displacingof an entity equal to the previously defined pre-stroke, display unit 38displays zero value. Then, the locking/unlocking device is operated,and, specifically, screw 80 is clamped onto the coupling surface 40 inorder to lock casing 35, and thus the entire gauging head, to support 67in the position that has been so determined. Upon completing thelocking, possible limited deviations with respect to the value displayedby unit 38 are compensated by operating adjustment potentiometers ofunit 38, per se known and not shown in the figures. At this point theapparatus is ready for checking and the master piece, that had been usedduring the zero-setting phase, is removed from the reference supportsand replaced by the piece 26 to be checked.

[0041] Upon contact occurring between feeler 25 and the surface of piece26, there occurs a rotational displacement of arm 5 in a clockwisedirection (with reference to FIG. 1) starting from the rest condition.This displacement causes a variation in the position of core 32 withrespect to the windings 34 of the transducer 27 and the latter providesan electric signal responsive to the deviation of the diameter size ofthe piece 26 taken into consideration for inspection, with respect tothe diameter size of the master piece.

[0042] If the nominal dimensions of the piece vary (within a relativelybroad range, that depends on the dimensions of the gauging head), thesame checking apparatus and the same supports for the piece referencecan still be used. This is effected by simply altering the position ofthe head with respect to support 67 by operating the locking/unlockingdevice (screw 80) and adjusting the axial arrangement of casing 35, byrepeating zero-setting operations similar to those previously described.

[0043] The particularly “light” structure of the arm-set of the head, inaddition to the absence of friction among the reciprocally movableelements of the transducer 27 ensures excellent performance at very lowforces (“measuring forces”) between feeler 25 and the surface of thepiece to be checked. This allows, among other things, to employ thegauging head for checking poorly stiff pieces, in other terms in thosecases in which a too high measuring force could deform the piece in thecourse of the measurement taking, and thus generate unreliable and nonrepeatable results.

[0044] A typical example is the flatness checking of a broad andflexible surface of the casing of an electronic apparatus in which it isnecessary to utilize a plurality of heads for achieving accuratemeasurements. If each of these heads applies to the piece a substantialforce, there may occur not only the piece deformation during thechecking operations, but also that the deformation be irreversible. Inorder to reduce the layout dimensions of the electronic apparatus, oftenthe amount of space between the casing and the circuit boards, housedtherein, that carry the electronic components, is very small. Therefore,it is necessary to check the flatness of the casing surface, but it isalso important not to deform the formerly mentioned surface in order toprevent the casing, once assembled, from contacting the electroniccomponents on the boards. Gauging heads like the one illustrated inFIGS. 1 and 2 are, thus, particularly suitable for checkings of thistype, especially thanks to the possibility of operating at low measuringforces.

[0045] According to a second embodiment of the invention, illustrated inFIG. 3, there is a structure a great many coincident with that of FIG.1, insofar as, among other things, the armset with the shaped element 1,the feeler 25, the mechanical limiting device 51, the compression spring45, the locking elements with the screw 36, and the support 67 with thelocking/unlocking device including screw 80 are concerned.

[0046] An axial-sliding linear gauge, for example, a cartridge head 81of a per se known type comprises a substantially cylindrical-shapedcasing 82, that houses the windings 83 and the ferromagnetic core 84 ofa differential transformer transducer device, a stem 85, axially movableand partially housed in casing 82, that carries at one end an additionalfeeler 86 and at the other end the core 84, thrust means including anadditional spring 87 that applies to stem 85 a thrust towards theexterior of casing 82, and guide means 88, housed in casing 82, forguiding the displacements of stem 85. The casing 82 of gauge 81 ishoused in holes 29 and 31 in the reference portion 3 of element 1 andthe axial position of the cartridge head 81 is determined, by the screw36 that operates on a coupling surface 91 of casing 82, as describedwith regard to the casing 35 of the transducer 27 shown in FIG. 1. Areference abutment element 89 made of hardened material, locked to thethreaded hole 23 of arm 5, comprises a flat surface 90 for remaining incontact with the additional feeler 86 of the cartridge head 81, ashereinafter described.

[0047] The shaped element 1 is locked to support 67 by inserting cable37 through opening 73, by inserting the casing 82 in hole 75 and thenlocking the cartridge head 81 to support 67 in the required position byoperating screw 80 to restrict the opening 73.

[0048] The functioning principle of the checking apparatus substantiallycoincides with what has been herein described with reference to FIGS. 1and 2.

[0049] When a zero-setting operation on a master piece is performed, theprestroke of the gauging head is firstly defined by adjusting, underrest conditions, the position taken by casing 82 of the cartridge head81 in the opening defined by holes 29 and 31. More specifically, theadditional feeler 86 (integral with the ferromagnetic core 84) isbrought into contact with the surface 90 of the reference abutmentelement 89, and the position of the casing 82 (integral with thewindings 83) is further adjusted until the required pre-stroke value isdisplayed by unit 38. At this point, screw 36 is clamped onto thecoupling surface 91 of casing 82 for locking the position of the latteron the integral element 1. Then, the gauging head is locked to support67 by inserting casing 82 of the cartridge head 81 in hole 75 andadjusting its axial position until the feeler 25 contacts the surface ofthe piece to be measured and, subsequently to a displacement thatrepresents the pre-stroke, the display unit 38 displays a “zero” valuereading.

[0050] The master piece is removed and replaced with a piece 26′ to bechecked and the checking operation takes place in the mannerhereinbefore described with reference to the first embodiment of theinvention. In the course of the checking operations, the additionalfeeler 86 of gauge 81 always remains in contact—urged by the thrust ofthe additional spring 87—with the surface 90 of the reference abutmentelement 89 and consequently displaces integrally with arm 5, exactly inthe same way as to what occurs, in the embodiment shown in FIG. 1, topin 28 that carries, by means of stem 30, the core 32 of transducer 27.In this way, the additional feeler 86 and the stem 85—rigidly coupled tothe feeler—undergo just substantially axial strains, caused by thedisplacements of arm 5. Thus, those transversal strains that occur, forexample, in known applications in which the feelers of cartridge headsdirectly contact pieces to be checked and expose the in ternalcomponents of the gauge to undesired strains, are so avoided.

[0051] From the foregoing description, the versatility of the inventionis evident. In fact, the same armset with the bent element 1 can beemployed in gauging heads with a friction free transducer 27 (FIG. 1)enabling an extremely accurate measurement taking at very low measuringforces, or else in an axial-sliding linear gauge (FIG. 3) or a gauge ofanother type, as, for example, a dial type gauge, whenever similardevices are available and other requirements are necessary (as, forexample, the need to prevent the armset of the linear gauge fromundergoing any transversal strains), though maintain in both cases thesame locking, positioning and zero-setting simplicity.

[0052] In fact, the housing defined by holes 29 and 31 and theassociated locking elements are dimensioned and arranged so as to allow,as previously described, the simple and rapid locking of both thewindings—housed in a suitable casing (35)—of a transducer (27) and“standard” size gauges. On the other hand, it is possible to couple—inan equally and obviously rapid and simple way—to the threaded hole 23 inarm 5, aligned with hole 21 that houses the feeler 25, either the pin 28carrying stem 30 and core 32, or the reference abutment element 89 withthe flat surface 90 for maintaining contact with the feeler of a gauge(for example, feeler 86 of the cartridge head 81).

[0053] Moreover, the manner according to which the head is locked to thesupport 67, besides providing flexibility and application simplicityadvantages, as hereinbefore described, does not need extremely accuratemechanical machinings of the surfaces of the integral element 1, that donot affect in any way the positioning.

[0054] In addition to versatility, one of the main advantages that theinvention provides is the simplicity and low costs for manufacturing thearmset of the head, specifically insofar as the material utilized, theimplemented structure, and the necessary operations are concerned. Infact, the shaped element 1 is formed by bending to a U shape a bar ofstainless sheet-steel, and achieving the fulcrum by drawing, forexample, by using a press for striking a blow to the sheet-steel bar,and subsequently grinding it. By drawing, there is obtained a workhardening of the material and hence an increase of the elastic range atthe point where it is desired to implement the fulcrum. The partundergoing the drawing is then ground for the purpose of obtaining therecess that enables to further lighten the fulcrum and so providelightness and low measuring force, typical characteristics of the head.

[0055] Moreover, as the material utilized does not have to undergo ahardening process beforehand, no subsequent antioxidant treatments ofthe head armset are necessary, and the material is substantiallyinsensitive, even in the case of very thin and yielding fulcra, to thenegative effects that the heating generated by the subsequent grindingoperation might have on the ultimate tensile stress of the material(tempering).

[0056] A further advantage that the heads herein described andillustrated provide is a specific high degree of precision and accuracy,thanks to the aligning between the straight line according to which thefeeler 25 substantially displaces and the one along which reciprocaldisplacement is among the parts of the transducer device (32,34;83,84)takes place.

[0057] Indeed, this allows the observance of the Abbe principle—wherebyin order to measure a length and benefit by all the measurement accuracyof the gauging instrument, it is necessary to arrange the formerlymentioned length along the detecting, or transduction axis. Furthermore,as it is not necessary to keep into account specific “arm ratios”, theprocessing operations in unit 38 are simplified and the detecting issubstantially insensitive to inaccuracies upon defining the rotationaxis by fulcrum 13 and to flexions of arm 5.

[0058] It is possible to modify the herein described head and checkingapparatus according to the present invention, without departing from thescope of the invention. For example, it is possible to manufacture thelimiting and/or thrust devices in a known way, that differs from whathas been described, or arrange them in another way.

[0059] In particular applications it is also possible to employ a feeleroff-set with respect to the point where it is coupled to the arm. Theshaped element can be manufactured by employing a material differentfrom the stainless sheet-steel and the hardening process can be attainedby following known processes that differ from the drawing process.

[0060] It is possible to employ even capacitive, or inductive type,transducer devices, manufactured in a different way from the one hereindescribed.

[0061] Furthermore, by means of a machining process according to thepresent invention, it is possible to manufacture an armset with anintegral element similar to the one illustrated and described, suitablefor applications differing from those illustrated and that can beemployed, for example, in absolute measuring heads.

[0062] Moreover, the herein described process for manufacturing thefulcrum also applies to the machining of armsets that have other shapes,as, for example, arm-sets with a plurality of fulcra and a so-called“parallelogram” type structure.

1. Gauging head suitable for coupling to a support (67) for the lineardimension checking of a mechanical piece (26) comprising a shapedelement (1) defining a first reference portion (3), a second portion(5), or arm, movable with respect to the first, and an intermediateportion (13), or fulcrum, between the first and the second portion, thatdefines a geometric axis of reciprocal rotation between said first andsecond portion, a feeler (25) fixed to said arm for contacting the pieceto be checked (26), and a transducer device (27;83,84) for providingsignals responsive to the position of the feeler with respect to thereference portion, including two reciprocally movable parts, a firstpart (34,35;82,83) thereof being stationary with respect to said firstportion of the shaped element, and a second part (32;84) being movable,together with said arm, with respect to the first portion, characterizedin that said first part of the transducer device comprises a casing(35;82) with an elongate shape, locked to the reference portion anddefining a coupling surface (40;91), said casing being adapted forlocking to the support (67) at said coupling surface for defining theposition of the shaped element with respect to the support.
 2. A gauginghead according to claim 1 , wherein said elongate shaped casing definesa transversal geometric axis of adjustment, the first portion of theshaped element comprising an opening (29,31) and locking elements (36)for enabling the locking of the first part (34,35;82,83) of thetransducer device to the reference portion of the shaped element, in aposition adjustable along said transversal geometric axis.
 3. A gauginghead according to one of the previous claims, wherein said first andsecond part of the transducer device comprise windings (34;83), housedin said casing (35;82), and a core made of ferromagnetic material(32,84), housed within the windings, respectively.
 4. A gauging headaccording to one of the previous claims, wherein said casing (35;82) ofthe transducer device has a substantially cylindrical shape.
 5. Agauging head according to one of the previous claims, wherein saidsecond part (32) of the transducer device is coupled to the arm (5) ofthe shaped element (1).
 6. A gauging head according to claim 5 , whereinsaid transducer device comprises a tubular sealing gasket (39) with endscoupled to said arm (5) and said casing (35), respectively.
 7. A gauginghead according to claim 3 , wherein the transducer device comprises anaxial-sliding gauge (81) that defines said substantiallycylindrical-shaped casing (82), and comprises a stem (85), axiallymovable with respect to the casing, that carries at one end said core(84) and at the opposite end an additional feeler (86), and thrust means(87) for urging said additional feeler to contact a surface (90)integral with the arm of the shaped element.
 8. A gauging head accordingto claim 2 , or claims from 3 to 7 as depending from claim 2 , whereinsaid feeler (25) is coupled to the arm of the shaped element in aposition that is substantially aligned with said transversal geometricaxis of adjustment.
 9. A gauging head according to one of the preceedingclaims, wherein the shaped element is made of bent sheet.
 10. A gauginghead according to claim 9 , wherein the shaped element is made ofstainless material.
 11. A gauging head according to claim 10 , whereinthe shaped element is made of stainless steel.
 12. A gauging headaccording to claim 11 , wherein said fulcrum is achieved by acompression and a subsequent grinding operation.
 13. A gauging headaccording to one of the previous claims, including thrust devicesbetween said arm (5) and said reference portion (3) with a compressionspring (45) that cooperates with said arm (5) and said reference portion(3).
 14. A gauging head according to one of the previous claims,comprising a mechanical device (51,57,59,61) for limiting the reciprocaldisplacements of said arm (5) with respect to said reference portion(3), with an element (51) coupled to one (3) of said first and secondportion of the shaped element and comprising abutting surfaces (51,59)for cooperating with the other (5) of said first and second portion. 15.Checking apparatus for the linear dimension checking of a mechanicalpiece (26), comprising a support (67), a gauging head with a shapedelement (1) for defining a first reference portion (3), stationary withrespect to the support, a second portion (5), or arm, movable withrespect to the first, and an intermediate portion (13), or fulcrum,between the first and the second portion, that defines a geometric axisof reciprocal rotation between said first and second portion, a feeler(25) fixed to said arm for contacting the piece (26) to be checked, anda transducer device (27;83,84) for providing signals responsive to theposition of the feeler with respect to the reference portion, includingtwo reciprocally movable parts, a first part (34,35;82,83) thereof beingstationary with respect to said first portion of the shaped element, anda second part (32;84) being movable, together with said arm, withrespect to the first portion, and a processing unit (38), electricallyconnected to the transducer device, characterized in that said firstpart of the transducer device comprises a casing (35;82) with anelongate shape, and the support (67) comprises an opening (75) and alocking/unlocking device (77,79,80) for housing said casing andadjusting the position of the shaped element with respect to thesupport.
 16. An apparatus according to claim 15 , wherein said elongateshaped casing defines a coupling surface (40;91) and a transversalgeometric axis of adjustment, the locking/unlocking device (77,79,80)cooperating with said coupling surface for locking, in an adjustable wayalong said transversal geometric axis, the position of the gauging headwith respect to the support.
 17. An apparatus according to claim 16 ,wherein said feeler (25) is coupled to the arm of the shaped element ina position that is substantially aligned with said transversal axis ofadjustment.
 18. An apparatus according to claim 17 , wherein said shapedelement is made of bent stainless sheet-steel.
 19. Process for machiningthe armset of a gauging, or measuring, head including an integralelement (1) that defines two reciprocally movable portions (3,5) and afulcrum (13) between said portions, including the following sequence ofsteps: arranging a bar of metal material, implementing the workhardening of an area of said bar, and reducing the thickness of the barat said area by grinding, for achieving said fulcrum and defining saidreciprocally movable portions of the integral element.
 20. A processaccording to claim 19 , wherein said area of the bar undergoescompression by means of a tool for providing said work hardening.
 21. Aprocess according to claim 20 , wherein the bar undergoes drawing on apress, for achieving a work hardening of said area.
 22. A processaccording to one of claims from 19 to 21, comprising additionaloperations for bending the bar in order to attribute a substantiallyU-shape to said integral element.